1. Field of the Invention
This invention relates to accelerator mass spectrometry, wherein particles to be identified are accelerated as a beam and passed through electrostatic and magnetic fields and defining apertures which remove from the accelerated beam all particles except those to be identified.
2. Description of the Prior Art
Carbon-14, a radioactive isotope of the element carbon, decays to Nitrogen-14 with a half-life of 5730 years. It is often employed as a radioactive tracer by introducing it in the form of a C-14 labeled compound which follows the path and progress of chemical or physical processes.
Unlike many of the other radioactive isotopes that are used as tracers, the activity of C-14 does not decay significantly for several thousand years. Thus, after a tracer experiment has been conducted, the samples themselves and any other waste that may have been produced as part of the experimental procedure (needles, gloves, etc.) must be disposed of in an acceptable manner that produces a minimal insult to the environment. Because of the comparatively long life of C-14, it is anticipated that even low-level wastes will require underground burial for several tens of thousands of years. Even if such burial sites can be found, these procedures are clearly time consuming and expensive and as a consequence it may be the case that the use of C-14 as a tracer is presently being seriously handicapped by the problems of disposal.
The detection of minute concentrations of a radioactive tracer by the observation of the radioactive decay of single atoms is a well understood art. However, as the half life of the tracer used increases, the time taken to carry out an efficient measurement, where most of the radioactive atoms are actually detected naturally increases; as an example for C-14 which has a half life of 5730 years, efficient detection of the introduced radioactive atoms is impossible unless the experiment can continue for about 10,000 years. For this reason trace measurements involving long-lived radioactivities are highly inefficient and require the use of large numbers of radioactive atoms, only a small fraction of which can be detected during the measurement.